The present invention relates to an asbestos-free disc roll.
In a step of producing glass sheets or in a step of heat treating thin plates or tubes of stainless steel, copper or brass, a so-called asbestos roll is used as a roll for transporting semi-products or articles thereon to be treated. This asbestos roll is ordinarily prepared by punching an asbestos plate having a thickness of about 6 mm into a disc, piling these discs so that a predetermined thickness is obtained, plunging a metal rod such as steel, which acts as a rotation shaft, through the piled discs, compressing the piled discs in the axial direction of the rotation shaft to form a dense structure and grinding the peripheral surface of the formed dense structure by a lathe or the like to finish the dense structure into a roll. This roll is a so-called disc roll.
When this disc roll is applied to the above-mentioned use, it is subjected to severe conditions such as being heated to a temperature of several hundreds to about 1000.degree. C. or higher, and therefore, the disc roll is required to have a high heat resistance property. With regard to this point, ordinarily used asbestos rolls are not completely satisfactory. The reason is that the thermal characteristics of asbestos constituting the roll are insufficient. More specifically, when asbestos is heated at 400.degree. to 800.degree. C. or a higher temperature, water of crystallization is released and contraction is caused. Moreover, the central rotation shaft expands at such elevated temperatures. Accordingly, linear cracks are readily formed in the axial direction of the rotation shaft and annular cracks are readily formed in the direction rectangular to the axial direction of the rotation shaft. When these cracks are once formed, a high-temperature furnace gas enters these cracks causing the cracks to grow at an accelerating rate, with the result that the asbestos plates peel off and fall away from each other. Furthermore, gaps are formed between the asbestos plates and the rotation shaft, and the position of some asbestos plates deviate, with the result that convexities and concavities called "stairs" are formed on the surface of the roll. The above-mentioned cracking, falling and formation of stairs results in the degradation of the quality of a product such as a glass sheet passed thereon as well as causing an irregular compression on the glass sheet causing the glass sheet to break. In case of the heat treatment of a thin metal plate, the surface of the roll having cracks or stairs formed thereon is printed on the softened surface of the metal plate being treated thereon and the surface condition of the plate is drastically degraded.
Furthermore, since asbestos dust particles are harmful to the human body, the asbestos roll has a major drawback in that special attentions must be paid in the production and use of the asbestos roll.
In order to obviate the foregoing disadvantage, disc rolls prepared without using asbestos plates, for example, disc rolls prepared by using ceramic fibers instead of asbestos, have been proposed. However, since ceramic fibers are more rigid and brittle than asbestos, it is impossible to increase the density of the roll by strongly compressing discs. Accordingly, a roll prepared by using ceramic fibers has the disadvantage that the roll is readily worn down. Furthermore, ceramic fibers ordinarily contain granules called shots, and if the shots appear on the surface of the roll, they are likely to damage a material being treated thereon.